This invention relates generally to electromagnetic energy absorbers, and more specifically to a radar energy absorber system that is used to eliminate false radar targets created by electromagnetic radar reflections from structures in the proximity of the radar. Such false targets are a hazard to air traffic safety and a source of confusion to air traffic controllers.
Air traffic control radar beacon systems (ATCRBS) serve a multiplicity of functions including aircraft identification and location, presentation of ground speed and altitude and other aircraft parameters. The operations, functions and general considerations of air traffic control radar beacon systems are discussed in the text entitled, "Introduction to Radar Systems" by M. I. Skolnik published by McGraw Hill in 1962. Further refinement and utility of the air traffic beacon system has been provided through the application of the Automated Radar Terminal System (ARTS) wherein a coded transponder response is processed by computer to attach identifying "flags" with appropriate information on the radar indicator for immediate controller use.
With increasing airport congestion, and with the use of ARTS, one problem that has become increasingly significant is that of false targets or ghost targets created by interrogator-transponder communication over a reflected signal path. Structures in the proximity of the radar provide alternative communication paths between the aircraft and the controller. As a result, a ghost or virtual image of a true target is presented on the radar indicator with its range determined by the time of propagation and its azimuth determined by the direction in which the radar antenna is pointing when reflections from the structure illuminate the true target. The resultant presentation is not that of the true target, but rather that of a false target generated by inadvertant interrogation of the aircraft beacon via the reflective structure.